docs: def Woldesemayat_Ghajar(x, rhol, rhog, sigma, m, D, P, angle=0, g=g):
      r'''Calculates void fraction in two-phase flow according to the model of 
      [1]_.
      
      .. math::
          \alpha = \frac{v_{gs}}{v_{gs}\left(1 + \left(\frac{v_{ls}}{v_{gs}}
          \right)^{\left(\frac{\rho_g}{\rho_l}\right)^{0.1}}\right)
          + 2.9\left[\frac{gD\sigma(1+\cos\theta)(\rho_l-\rho_g)}
          {\rho_l^2}\right]^{0.25}(1.22 + 1.22\sin\theta)^{\frac{P}{P_{atm}}}}
          
      .. math::
          v_{gs} = \frac{mx}{\rho_g \frac{\pi}{4}D^2}
          
      .. math::
          v_{ls} = \frac{m(1-x)}{\rho_l \frac{\pi}{4}D^2}
          
          
      Parameters
      ----------
      x : float
          Quality at the specific tube interval []
      rhol : float
          Density of the liquid [kg/m^3]
      rhog : float
          Density of the gas [kg/m^3]
      sigma : float
          Surface tension of liquid [N/m]
      m : float
          Mass flow rate of both phases, [kg/s]
      D : float
          Diameter of the channel, [m]
      P : float
          Pressure of the fluid, [Pa]
      angle : float
          Angle of the channel with respect to the horizontal (vertical = 90), 
          [degrees]
      g : float, optional
          Acceleration due to gravity, [m/s^2]
  
      Returns
      -------
      alpha : float
          Void fraction (area of gas / total area of channel), [-]
  
      Notes
      -----
      Strongly recommended.
          
      Examples
      --------
      >>> Woldesemayat_Ghajar(0.4, 800., 2.5, sigma=0.2, m=1, D=0.3, P=1E6, angle=45)
      0.7640815513429202
  
      References
      ----------
      .. [1] Woldesemayat, Melkamu A., and Afshin J. Ghajar. "Comparison of Void 
         Fraction Correlations for Different Flow Patterns in Horizontal and 
         Upward Inclined Pipes." International Journal of Multiphase Flow 33, 
         no. 4 (April 2007): 347-370. doi:10.1016/j.ijmultiphaseflow.2006.09.004.
      '''
      vgs = m*x/(rhog*pi/4*D**2)
      vls = m*(1-x)/(rhol*pi/4*D**2)
      first = vgs*(1 + (vls/vgs)**((rhog/rhol)**0.1))
      second = 2.9*((g*D*sigma*(1 + cos(radians(angle)))*(rhol-rhog))/rhol**2)**0.25
      third = (1.22 + 1.22*sin(radians(angle)))**(101325./P)
      return vgs/(first + second*third)